2 Answers
2

Or, to put it another way, any flat note you might want is covered by the four "settings" of a chromatic harmonica: no-side-key or with-side-key, each used with "blow" or "draw" (i.e. breathe-out or breathe-in). See this for a list of pitches when using these "settings".

EDIT: Just a couple of extra bits of info…

You can of course bend notes flat on chromatic harmonica, although there are limitations to this technique when compared to bending notes on a diatonic harmonica. However, by definition, chromatic harmonica allows all 12 chromatic pitches to be played without using this technique. Instead, this technique is used to add character and inflections of pitch; these need not be changes by exact semitones, but can be arbitrary changes of pitch, giving the "notes-between-the-notes". A good analogy would be guitar playing; all 12 chromatic pitches can be played using a standard technique, but use of bends and vibrato arm allow changes of pitch (either by exact semitones or other arbitrary distances), too.

Although the tuning you refer to seems to be considered standard, there are other tunings used for chromatic harmonica. In particular, Irish Tuninglowers the pitch of both blow and draw notes when depressing the side-key.

Just two quick observations: (1) "all flat notes are sharp or natural notes" in equal tempered tuning, not necessarily in other temperaments. (2) Harmonica will let you "bend" notes by overblowing, which may permit reaching some of those alternatives.
– keshlamJun 7 '14 at 5:31

@keshlam - most of the time, particularly in the Western world, we play using equal temperament. Other temperaments maybe belong where they were before we compromised to what has become 'industry standard'.
– TimJun 7 '14 at 6:11

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That's true of most recent Western music. Not true of blues, nor of earlier forms. Not even true of all recent music; there are performers who take full advantage of the possibilities of other temperaments. I think it's worth noting that although the modern harmonica is designed around equal temperament, it can reach somewhat outside that space. (You don't have to go back very far, either. My own instrument, an Anglo concertina, was almost certainly not equal-tempered when it left the factory though it has been retuned since.)
– keshlamJun 7 '14 at 6:18

@keshlam - with blues, the instruments are tuned to equal temperament even though notes are often bent to produce ones 'in the cracks', nevertheless they are rarely tuned to any other tuning.My point was that having, for instance, an instrument that plays G# out of tune to another's Ab is impractical. Possibly proved by your re-tuning the concertina.I'm well aware of the phenomenon - it just has no practical use in ensemble works - unless one is looking for authenticity in early Baroque etc. tunes.
– TimJun 7 '14 at 7:46

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@Tim: as "the original Blues instruments" I'd consider the human voice, which is not tuned in any temperament (most definitely not 12-edo), along with Blues harp (diatonic), Diddley bow (untuned), and slide guitar. Sure enough adaptions for piano and banjo / spanish-style guitar would quickly appear, but that's just approximations. "An instrument that plays G# out of tune to another's Ab is impractical" – no it isn't, e.g. flutes and clarinets certainly do that (though the player may trim manually). And let's not start with string instruments.
– leftaroundaboutJun 7 '14 at 10:13